I'm new to PDMG, finally got a computer that can handle the PDMG747 (I think). I'm trying to familiarize myself with the FMC and can't seem to find a CO Route in the FSX-PDMG FlightPlans folder for KJFK to KSEA. Is there a location in PDMG or AVSIM where one can get additional routes that will work within the PDMG flightplans folder and/or their FMC.

Yes there are some flightplans available. Best to search under the flightplan section within the file area. Something to consider is that the FMC uses an updatable database in which all the locations of waypoints/VORs/airports etc are stored. A new "cycle" of the database becomes available each month in the real world, and luckily to us, a company called Navigraph makes the data available to us simmers for a small charge. You can download the specific AIRAC cycle for all PMDG payware and it automatically installs into the fmc. Obviously flightplans change as the navdata changes, and so airlines have a nice big office full of people who are responsible for creating and checking flightplans so that a pilot can simply upload it to the fmc using the CO route function.Once you have got your head around the Queen, then maybe you could try having a go at making your own flightplans for your flight. There are some payware programs such as FSPlan which let you create a flightplan manually (or automatically if you want) and then the program saves the flightplan into the PMDG folder so you can import it into the FMC using the CO Route function.

If I recall correctly, the Boeing FMC logic does not check the database for the existence of a flight plan when you enter the DEP and ARR airports (like the J41 and MD11 do). You would have to give it the proper file name for it to go looking for it (in the case of PMDG's default routes, they're mostly [iATA][iATA]001.rte, so you would enter something to the effect of JFKSEA001 in the COROUTE boxes).The FLIGHTPLANS folder location is here (for Win 7, which I see you have as well):C:\Program Files (x86)\Microsoft Games\Microsoft Flight Simulator X\PMDG\FLIGHTPLANS